In February 2013, the asteroid 2012 DA14 flew past the Earth closer than many of the Earth’s geo-stationary satellites. Although not visible to the naked eye many telescopes were fixed towards the skies in a hope of catching a glimpse of this celestial fly-by. Many other people watched live webcasts of the asteroid as it came just 27 000km away from the Earth. It was never thought that this asteroid was going to cause any harm. However on the same day, coincidentally and unrelated a huge meteor streaked across the sky over the Ural Mountains in Russia. The sonic boom of the fireball sent shockwaves through the nearby town of Chelyabinsk. Fortunately no fatalities were caused, although over 1000 people were injured (mostly by broken glass). If a larger asteroid were to have crashed into the Earth it could have caused more disastrous consequences…
Throughout history the Earth has been pelted with various sized space junk both natural and man-made. Most of these are quite small or cause relatively localised damage over a particular area or have been sorted them out by Bruce Willis . Thankfully, throughout the human species’ life span falling asteroids or large impacts have not killed anyone. However, around 65 million years ago an asteroid or comet about 10km (6 miles) wide caused global extinction for around 70% of all life when it crashed into the Earth. This extermination is widely known to have marked the end of the Age of Dinosaurs or otherwise known as the K-T event (Cretaceous-Tertiary/Paleogene K-Pg extinction event).
The dinosaurs were the dominant group of animals to roam the Earth for 180 million years throughout the Triassic, Jurassic and Cretaceous periods (245 million-65 million years ago). Various theories on the cause of their extinction (yes, I do know that that birds are technically dinosaurs too, but the ‘classic’ dinosaurs like sauropods and big theropods are all gone) have been proposed. Changes in global volcanic activity, climate change or the large asteroid impact are all potential culprits or even a hybrid theory that perhaps a combination of events contributed to demise of the dinosaurs. Ultimately whether the sole cause or not, a large asteroid impact caused a major change on Earth.
Evidence to suggest a major impact, the Alvarez Hypothesis, is located many layers beneath the current Earth’s surface. The K-T boundary is the time between the end of the Cretaceous period and the start of the new era. This boundary can be identified in rocks under many layers of sediment. In 1980 the researchers Luis Alvarez, his son Walter Alvarez, Frank Asaro and Helen Michels identified the layer dating back 65 million years circa the time of the impact and noticed it contained high levels of the element iridium. Iridium is an element which is naturally rare on the Earth but is a common component of asteroids and meteorites. Another discovery within this layer where levels of soot discovered which would be expected after fires caused by a major impact. As well as this, within the rock at this level are crystals or pieces of quartz that have been altered or fractured expectant of being subjected to a major explosion. In the surrounding areas, levels of ejected matter, like glass tektites were found. This commonly happens when a celestial body hits the ground with great impact and turns the soil and sand into glass.
All of these factors point to a suspected impact event but without an obvious crater the Alvarez hypothesis met with opposition. Such a major occurrence would surely have been discovered or documented but it wasn’t for another 10 years that evidence confirmed a large crater at Chicxulub on the Yucatan peninsula in Mexico. At this location there was plenty of shocked quartz and tektites. Hidden for years under many layers of sediment was the 180km (110 mile) diameter of a crater, finally there was proof of a large asteroid impact. First proposed in the 1970s it wasn’t until Alan Hildebrand came onboard, that this impact crater was dated to 65 million years and became the missing piece of the puzzle.
It makes sense now to link the Chicxulub impact crater with a large asteroid that impacted 65 million years ago. However, such a severe impact would not have only left a huge hole in the ground but caused other devastating consequences. Most asteroids hitting the Earth do so at speeds of 10-20 km per second. The speed of the object as well as the mass of this asteroid (some asteroids have high percentages of iron in their makeup-therefore very dense) is responsible for such energy being forced into the ground (Kinetic energy= ½ x mass x velocity2). The impact would have been the equivalent of 100 000 billion tonnes of explosives hitting the Earth or the equivalent of a billion atomic bombs dropped on the Earth. It is thought that so much dust and dirt was dislodged from the ground that it filled the atmosphere for months blocking out the sunlight. Therefore plant life died and an important element of the food chain was eliminated. The darkness not only would have killed planets but also would have been devastating for plankton also an integral part of the food chain. Animals living on the surface like the dinosaurs were wiped out however some mammals that were able to hide or hibernate were able to survive.
Up to month after impact a haze would have remained in the air. Some scientists believe it may have taken up to 1000 years for the air to clear. However on a positive note the mammals that did survive which were likely to be rat-sized or slightly larger paved the way for life today to thrive and survive. If the dinosaurs had survived perhaps humans may have been just at the part of the food chain an afternoon snack for the T-Rex!
Scientists believe that such a devastating event is likely to happen to the Earth every 100 million years perhaps smaller ones causing localised explosions occurring every few hundred years like in Russia last month. So it is unlikely that we might have cosmic extinction in our lifetimes. Many near-Earth objects are monitored closely and in the future if astronomers spot one as large as 10km we’ll hopefully have developed the technology to divert it or perhaps the chaos may led way to a new more powerful species evolving.
(Article by Martina Redpath, Education Support Officer)